Use of pre-sorted plastic material wastes and process for producing a granular material as a filter for the purification of sewage

ABSTRACT

A granular material for use as a filter in the purification of sewage. The granular material is comprised of pre-sorted and cleaned plastic material wastes. A process for producing the same is provided.

[0001] The invention concerns the ecologically meaningful use ofpre-sorted plastic material wastes and a process for producing agranular material as a filter for the purification of sewage and wastewater.

[0002] The use of plastic material wastes, in particular those whichhave been pre-sorted and/or purified, is known in the state of the art,as well as various processes for producing a granular material made upof a single kind of material, as a filter for the purification of sewageand waste water. As is known, large amounts of plastic material wastes,in particular also domestic packaging, are recycled in terms of thematerial involved. The Deutsche Gesellschaft für KunststoffrecyclingGmbH, referred to for the sake of brevity as DKR, implemented aprocedure for suitably splitting up those various plastic materials.There is a foil or sheet fraction, a plastic bottle fraction, an EPSfraction, a cup fraction and a mixed plastic material fraction. Residuesare put to use by thermal processes, for example by the production ofenergy by incineration. Thus DSD (Duales System Deutschland) alreadyrepresented in 1997 a utilisation quota of 86%, as is referred to in thenewspaper ‘DIE WELT’ of Feb. 5, 1999. However the DSD-DKR system alsopresents itself as being more and more market and economy oriented. Ifat the present time there are still loss-making quotas of DM 500.00/mtfor the processors which are certified in the DSD-sector, that will infact change in the next few years.

[0003] Naturally large corporate groups with enormous levels ofexpenditure are in a position to satisfy the qualitative wishes of somelimited customers, inter alia also abroad. Nonetheless the market forthe DSD material still remains limited. The sole reason are for exampleproblems with dealing with materials of a single kind in each case,certain odorous fragments and the difficulty of the technicalspecification which still remains the same.

[0004] There is therefore a need at the lowest possible level ofexpenditure to produce a simple and ecologically meaningful product,starting from a basic raw material which is continuously available andwhich, unlike the situation with tubes or flanges which can be producedfrom the DSD granular material, sets only low levels of demand in termsof quality.

[0005] WO 94/26086 also discloses plastic granular materials which areproduced from polymer materials which are not homogeneously extruded byan extruder and are used in water treatment installations for thecleaning and purification of sewers or sewage and waste water. It willbe appreciated that the initial plastic material products used inaccordance with that particular process are relatively expensive, andfor that reason the industrial use thereof, outside Great Britain, hashitherto not taken place on a greater scale.

[0006] As a countermove to these high-qualified plastic materials theinvention seeks to afford a remedy insofar as it opens up a new purposeof use for plastic material wastes and in particular those whichoriginate from the dual system in Germany and Europe.

[0007] The aim of the present invention is to provide a process based onthose wastes for producing a granular material as a filter for thepurification of sewage, which affords an inexpensive end product in aparticularly simple and rapid fashion.

[0008] The process steps according to the invention are as follows:

[0009] a) Procuring and providing this plastic material waste, inparticular that from the bottle fraction of the Duales SystemDeutschland DER GRÜNE PUNKT,

[0010] b) cleaning and chopping that plastic material waste and thendrying same,

[0011] c) heating same at about 280° to the molten state,

[0012] d) extruding same, in particular at degressive temperatures, byway of a screw or cascade extruder, in particular at a rotary speed ofbetween 260 and 300 rpm, and a mass pressure of between 130 and 150Kp/cm², and

[0013] e) cooling the molten material and cutting and/or sieving off thegranular material in the desired length.

[0014] Surprisingly therefore it has been found that in actual factpre-sorted plastic material waste as occurs with DSD in the form of awaste product, can be used not only as a recycling product but also agranular material produced therefrom can be used as a filter for thepurification of sewage. That is a particularly ecological form ofexploitation which affords an extremely inexpensive starting material.Hitherto the men skilled in the art have not thought of such a systemwhich operates in a circulatory mode, on the basis of regularlyavailable DSD granular materials, as apparently the principle accordingto the invention of purifying waste (sewage) with waste' involves amajor inhibition.

[0015] While in accordance with the invention a cascade extruderoperates without peroxide, it is advantageous in terms of the processfor a small amount of peroxide to be added for cross-linking purposes tothe DSD base product in the screw extruder, giving a homogeneous endproduct. Advantageously, for that purpose only between about 10 and 20and in particular 15% by weight of the DSD plastic waste material ismixed with the peroxide additive, for example dicumyl peroxide at 40% inPE, or peroxide-bearing waste materials, in particular chopped or groundfloor heating tubes, in order to achieve the largest possible surfacearea for the granular material, whereby the colonisation ofmicro-organisms is possible and the longevity of the granular materialis increased.

[0016] The degressive temperature control in conjunction with theperoxide provides for a resistant surface area for the granularmaterial, which is as large as possible and which permits micro-organismcolonisation. The peroxide also affords the advantage that in this casewith the longevity in question this involves a system which afterpurification can in practice be used repeatedly.

[0017] A preferred embodiment of the operating procedure according tothe invention is described in greater detail hereinafter:

[0018] preparing a mixture in a mixing silo:

[0019] about 85% by weight of DSD material, cleaned and dried groundbottle material,

[0020] about 15% by weight of PE compound (contains about 2% peroxide);

[0021] alternatively:

[0022] about 15% by weight of PE ground material from floor heatingtubes (note: in the case of cascade extruders, no 15% by weight admixingis necessary)/(the term cascade extruders is used to denote twoextruders which are connected together);

[0023] heating the extruder;

[0024] starting the extruder with adjustment of the heating zones(falling degressively from 270° C./melting of the introduced groundbottle material—200° C.) and of the cutting tools for regulating thegranular material size;

[0025] starting degassing (in the case of cascade extruders doubledegassing possibly necessary);

[0026] addition of 1% black master batch (that is to say a coloradditive by way of a metering installation, color is actually notnecessary but improves optical aspect/impression;

[0027] setting the screw rotary speed, individually according to therespective type of extruder, in most cases at 300 rpm;

[0028] a mass pressure of about 130 kg/cm² is correspondingly reached;

[0029] extruding the mixture by way of an extruder by way of a 400μsieve;

[0030] extrusion through a 1.5 mm apertured plate. A man skilled n theart can envisage other sizes;

[0031] cooling the granular materials by way of a water bath;

[0032] cutting and sieving off the oversizes and undersizes of thegranular materials;

[0033] sucking off into a storage silo;

[0034] bagging from the storage silo in for example 1200 kg bags; and

[0035] setting down the bag on a wooden board.

[0036] The bottle fraction of the DSD was investigated on the basis ofvarious samples, the results of which are set out hereinafter: Plasticmaterial bottles Specification Purity Impurities Bottles ≦ 5 liters min94% IL metal volume content (for specification glass example shampoo max3% impurities paper bottles, detergent max 3% other foreign materialssuch as bottles, domestic plastic material rubber, textiles, wood,stones cleaners) packagings composite materials such as plasticmaterial-aluminum (drinks cartons etc) non-packagings of plasticmaterial (special agreements remain reserved)

[0037] 1st sample - regranular material from DSD bottle fraction(green-grey granular material) Analysis values Test for Test procedureTest result PVC RFA <0.05% Polyamides Formic acid Non-detectableextract/IR Polystyrene, ABS, Chloroform 1.44% polycarbonate, extract/IRplasticiser, wax etc Fillers, glass fibers, Ignition residue at 0.920/0inorganic 550° C. (DIN 53 accompanying 568) materials Comments Thechloroform extract predominantly comprises an aliphatic carboxylic acidester. It was not possible to detect thermoplastic impurities such aspolystyrene, ABS, polycarbonate etc. The extraction residue comprises amixture of polyethylene (main component) and marked amounts ofpolypropylene. Impurities are not detectable IR-spectrometrically.Summary After consideration is given to the impurities determined in 5there is a content of polyolefins (PE/PP) in sample A of ≧97%.

[0038] 2nd sample - ground material from DSD bottle fraction (from afurther manufacturer) Analysis values Test for Test procedure Testresult PVC RFA <0.05% Polyamides Formic acid Non-detectable extract/IRPolystyrene, ABS, Chloroform 1.14% polycarbonate, extract/IRplasticiser, wax etc Fillers, glass fibers, Ignition residue at 1.03%inorganic 550° C. (DIN 53 accompanying 568) materials Comments Thechloroform extract predominantly comprises an aliphatic carboxylic acidester. It was not possible to detect thermoplastic impurities such aspolystyrene, ABS, polycarbonate etc. The extraction residue comprises amixture of polyethylene (main component) and marked amounts ofpolypropylene. Impurities are not detectable IR-spectrometrically.Summary After consideration is given to the impurities determined in 5there is a content of polyolefins (PE/PP) in sample A of ≧97%.

[0039] The process according to the invention therefore shows that theplastic material used does not have to be sterile and new for each useand precisely not for use as a filter, but on the contrary the productsdescribed and claimed can be employed for that purpose.

[0040] Besides the described possibility of using in particular plasticmaterial wastes from the bottle fraction, it is also possible to usemixed plastic materials.

[0041] If problems arise by virtue of fluctuations in density in themixed plastic materials, such fluctuations in density can be compensatedby the addition of fillers such as for example chalk so that theresulting granular material grains are always of the desired density andcan be suspended in water.

[0042] The invention also includes the possibility of not only preparingthe granular material as a filter substrate but also as a carrier formicro-organisms, by means of which then a fluid can be treated in thedesired manner if the granular materials are colonised together with themicro-organisms for example in a water treatment apparatus.

1. Use of pre-sorted, cleaned plastic material wastes, substantiallycomprising polyethylene and/or polypropylene, for the production of agranular material which is used as a filter for the purification ofsewage.
 2. Use as set forth in claim 1 characterised in that thegranular material is of a grain size which is in the range of between0.5 and 5 mm.
 3. Use as set forth in claim 2 characterised in that thegrain size is between about 3 and 4 mm.
 4. Use as set forth in one ofthe preceding claims characterised in that the granular material is of asubstantially cylindrical shape, with a cylinder diameter of betweenabout 1 and 5 mm and a cylinder length of between about 1 and 5 mm. 5.Use as set forth in one of the preceding claims characterised in thatthe granular material has a structured surface.
 6. Use as set forth inone of the preceding claims characterised in that the granular materialis in the form of a sleeve.
 7. Use as set forth in one of the precedingclaims characterised in that the granular material is of a very highspecific surface area which is in the region of more than 1 cm²,preferably more than 2 cm² per granular material particle.
 8. Use as setforth in one of the preceding claims characterised in that thepre-sorted plastic material wastes are substantially produced from oldplastic material bottles consisting to a very great extent ofpolyethylene and polypropylene.
 9. Use as set forth in one of thepreceding claims characterised in that the plastic material wastesrepresent a mixture of at least two polymer materials forming ahomogeneous mixture.
 10. Use as set forth in one of the preceding claimscharacterised in that the granular material particles are of a densityof between about 0.700 and 0.980 g/cm³, preferably between 0.890 and0.940 g/cm³.
 11. Use as set forth in one of the preceding claimscharacterised in that the tensile strength of the granular materialparticles is approximately in the range of between 15 and 70 MPa and thegranular material particles expand under a tensile loading by betweenabout 5 and 20% of their initial size.
 12. Use as set forth in one ofthe preceding claims characterised in that the granular material has amodulus of elasticity of between about 650 and 1500 MPa, preferablybetween about 900 and 980 MPa.
 13. Use as set forth in one of thepreceding claims characterised in that the granular materials have alens-shaped particle form.
 14. Use as set forth in one of the precedingclaims characterised in that the granular material has cavities whosetotal volume is less than 10% of the total volume of the granularmaterial particles.
 15. Use as set forth in one of the preceding claimscharacterised in that the polypropylene proportion in the granularmaterial is at least 5% and preferably between about 10 and 20%.
 16. Useas set forth in one of the preceding claims characterised in that anaddition of between about 0.01 and 5% by weight of a peroxide, withrespect to the total weight of the plastic material, is added to thepre-sorted plastic material wastes.
 17. Use as set forth in claim 16characterised by an addition of between about 0.1 and 0.5% by weight ofa peroxide, with respect to the total weight of the plastic material.18. Use as set forth in one of the preceding claims characterised inthat the plastic material wastes from which the granular material isproduced are cleaned.
 19. Use as set forth in one of the precedingclaims characterised in that the added peroxide is added in ground form.20. Use as set forth in one of the preceding claims characterised inthat the plastic material wastes from which the granular material isproduced contain a plurality of mixed plastic materials.
 21. A processfor producing a granular material which is suitable as a filter for thepurification of sewage, comprising the following steps: a) procuring andpreparing pre-sorted plastic material wastes, in particular those fromthe Duales System Deutschland DER GRÜNE PUNKT, b) cleaning, chopping anddrying said plastic material waste, c) heating same to the molten state,d) extruding same through a screw or cascade extruder, and e) coolingthe molten material and cutting the granular material at the desiredlength.
 22. A process as set forth in claim 21 characterised in thatprior to step e) there is an addition of between 0.1 and 0.5% by weightof peroxide or peroxide-bearing wastes at the extruder head.
 23. Aprocess as set forth in claim 22 characterised in that only between 10and 20% by weight of the plastic material waste is mixed with between 1and 3% by weight of peroxide and then homogenised with between 80 and90% by weight of the initial material of plastic material waste.
 24. Aprocess as set forth in claim 23 characterised in that 15% by weight ofthe plastic waste material is mixed with between 1 and 3% by weight ofperoxide and 850% by weight of the starting material of plastic wastematerial is mixed and homogenised.
 25. A process as set forth in claim22 or claim 23 characterised in that the temperature in the extruder isdegressively adjusted, more specifically at the inlet in the range ofbetween 250 and 300° C. and at the extruder head between 180 and 200° C.26. A process as set forth in claim 21 characterised in that a cascadeextruder with a 400 mm sieve and a 2.5 mm apertured plate is used. 27.Granular material which is used as a filter for the purification ofsewage, produced from pre-sorted plastic material wastes which contain aplurality of mixed plastic materials, wherein the density of thegranular material is approximately in the range of between 0.70 and0.980 g/cm³, preferably in the range of between 0.890 and 0.940 g/cm³.28. Granular material as set forth in one of the preceding claims.